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What relationships exist between pressure systems and fronts?
I'm a student studying weather systems and believe I understand that high pressure systems are areas of colder descending air that tend to dissipate cloudiness and provide good weather and clear skies. Low pressure systems are areas of warmer rising air that can lead to the formation of clouds, perception, thunderstorms etc.
I've also studied the different types of fronts (cold, warm, occluded) and the types of weather they may bring.
Where I'm confused is what is general relationships between pressure systems and fronts. If I'm looking at a surface analysis chart to get a big picture understanding of the weather, do I view pressure systems and fronts independently? I know that if I see low pressure and a cold front to expect bad weather but could I see a cold front next to a high pressure system (and what would this mean)? I'm confused on how to consider both pressure and frontal systems together to understand whats going on. Any examples of how to interpret surface analysis charts would be appreciated
Thanks for the help!

So, the number one key to understanding weather is that it is just stupidly, immensely complicated. Looking at a surface analysis tells me nothing about upper air goings-on, and vice versa. So most of what you learn in basic aviation weather is overly simplistic. I’ve found that dedicated weather courses such as NWS’s Jetstream are far more comprehensive in teaching you how to understand macro weather patterns.
Remember that a front is simply a boundary between 2 air masses. How these air masses are interacting at that frontal boundary is what determines the type of front (cold, warm, etc). The actual weather involved is dependent on tons of factors, including moisture, stability, the amount of lifting action produced at the front, etc. Cold fronts don’t always produce squall lines of thunderstorms, for example. Usually, however, there will be some sort of shift across the boundary, most noticeably in temperature but also in other ways as the new air mass comes overhead.
As to how fronts interact with high and low systems, so much depends on a variety of factors. A cold, high pressure air mass plowing underneath a warm lower pressure air mass (this is a cold front) is producing atmospheric lift, but if the air is stable you won’t get any sort of precipitation associated with it. What is the pressure status of the upper atmosphere? An upper level low trundling along up there can wreak all kinds of havoc regardless of the surface conditions. This is why these huge prediction models like GFS and HRRR are used to make forecasts. They can synthesize this data comprehensively to help meteorologists make predictions.
From an aviation perspective, I wouldn’t worry too much about becoming your own big-picture forecaster, at least not until you take a course in meteorology. Tons of free resources can do this for you with far more knowledge and expertise. The way weather is usually taught to private pilots sets new students up for potentially dangerous mistakes as they mis-identify whats actually happening in the atmosphere.
Let the experts and their products work for you as you learn. A great resource is the forecast discussions on AWC and on the NWS website. They are great tools to get a big picture understanding of the conditions in your region. I very rarely fly without reading them! In time, you start to begin to put the whole picture together.
Sorry for the long answer. Hope this helps!

The front is what gives birth to the frontal depressions in the first place. These depressions contain their own portions of the front; that portion then moves along with the circulation in the depression. You can see that in this surface pressure chart of the polar front.

Image source


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Is there a legal requirement for planes to start from the ground?
If I could somehow store a plane inside another plane, would I be allowed to start the second plane somewhere in the air? Maybe different countries have different laws for this kind of aviation?
I know that this is technically at least challenging if not impossible, I was just wondering if I would even be allowed to do this.
Bonus Question: How would the pilot communicate this to the authorities?

This has bee done decades ago by organisations known for doing it without asking for permission.

Tow launching a glider is sort or almost what you're asking

At least in the US, this is perfectly legal. There have been quite a few such aircraft in history.
However, an aircraft docking and undocking from another is so rare that there's no standard way of communicating it with ATC. So you'd have to explain what you're doing in plain language. (And then you'd have to explain it again when the confused controller replies, "What?") If I were flying such a mission, I'd contact the local FSDO ahead of time to explain it, so that they can forward the information on to the local ATC facility to cut down on confusion.

I'm pretty sure that there aren't too many "What????" questions from controllers at KMHV these days...

It is possible- which is a strategy that is commonly thought of in conjunction with space tourism. You can not only start a plane in air using another airplane but also start a hybrid rocket from an airplane in air. For that look up SpaceShipOne and its carrier aircraft.

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Why do fighter jets make a whistling noise when landing and taking off?
Lately, I was watching fighter jets (F-16s and F-35s) from very close (fascinating!) and heard for the first time the "whistling noise" when they were landing and taking off. I expect it has something to do with the compressor of the fighter jets, but I am not sure because I found some sources on the Internet and they all actually say something different:

Quora
abovetopsecret
Reddit

I was wondering if anyone could explain with some good sources why this "whistling noise" happens and maybe its functionality?

It depends on the definition of the "whistle" that you are talking about. Both Michael Hall and Niels Nielsen are correct for what they consider "whistle". I personally think that you are talking about a different kind of whistle; the hydraulic actuators of the variable duct exhaust systems are very powerful and produce a short high pitch noise when operating. Unless very high power is being used, this noise can easily be heard over the engine noise. Is the noise that you are talking about continuous or brief? If it is brief, then it's definitely the hydraulic actuator noise.

When the plane has its gear down and its flaps deployed, the airflow over the open landing gear wells and across the gear struts and whatnot can produce a distinct whistling noise that is strongly modulated by speed and angle of attack.
Even small planes like the Piper Cub "whistle while they work" and you can hear this when a Cub pilot cuts power on approach. The engine noise dies off but the whistling persists.
The most famous whistler is probably the P-51. there are many youtube videos of P-51's doing low passes and steep pull-ups at high speed, and when the AoA is just right they make a very loud and creepy-sounding whistle noise.

Turbines have a characteristic whining sound that is most likely what you are hearing.  You can hear the same effect on a turbocharged car when the turbine spools up.  The sound itself isn't functional, it is simply a byproduct of the compressor working as it normally does.

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Are there any failure-proof instruments on commercial airliners?
Let's assume worst case scenario - nighttime over the ocean, complete vacuum failure, perhaps complete electrical failure (in a "fly-by-pulley" plane perhaps), or at least avionics failure.
Is there any instrument on board capable of providing, at very least, horizontal situation indication, so the plane can safely get to a lit area for visual navigation?
Even in my car, I have a 25 cent toy spherical compass in water, that, at very least, can give me such information.  Even a handheld phone has good enough gravity sensors for this. for Is there anything available on the flight deck like this?

What is a "horizontal situation indication"? You mean if the aircraft is flying level or not? Then no, a wet compass or phone cannot do that in an airplane. There is no "failure proof" instrument, that is why most commercial aircraft have multiple instruments that do the same thing using different methods.

@RonBeyer a wet compass no, but airliners are equipped with one "old fashioned" version of each instrument, including the artificial horizon.

@Federico I don't believe that is accurate, if you mean vacuum gyro driven by "old fashioned". For example, see the A380 cockpit. Notice an artificial horizon on the left is an LCD screen, no "old fashioned" instruments...

As well, an old-fashioned HSI would fail with vacuum failure, no?

@RonBeyer, yes, some sort of HSI.   Why couldn't a phone or wet compass do it?

@aAaaaAaa Because when you bank, you can turn at 1G which means that the "gravity" vector banks with the aircraft. Phones don't sense "gravity", they sense a force vector. Compasses lead/lag turns and have the same "gravity" issues phones have, they don't point down, they align themselves with the force vector pulling them down, which changes in a turn.

@RonBeyer I was more familiar with the older 320, I admit https://airandspace.si.edu/webimages/highres/WEB10778-2007h.jpg

Phone or wet compass won't give you anything but a combination of 'down' and whatever acceleration the aircraft is providing. Assuming that true 'down' is what's pulling you into your seat is a deadly mistake (see Graveyard Spiral).

@RonBeyer couldn't a GPS device calculate groundspeed and altitude, and infer from that, at very least, rate of descent or ascent? Not quite horizontal situation, but if it shows 50knots and descending, pilots could probably infer they are in a descending flat stall....

So which is easier, to make something never fail or to make two thing that never fail at the same time?

"couldn't a GPS device calculate groundspeed and altitude ... if it shows 50knots and descending, pilots could probably infer they are in a descending flat stall" Except when they're not. Stalling is about airspeed and angle of attack, not ground speed. In extreme situations, it's even possible to fly a ground track that moves you backwards, especially in a small plane, and be nowhere near a stall of any kind. Just watch out when the wind shifts... And if you have complete electrical and vacuum failure, how do you propose to power said GPS? What about the flight controls?

Have you ever piloted an aircraft? (Just to say it: being a pilot is not a prerequisite for participating on Aviation SE, but you'll generally be expected to have some idea of aviation matters.) Adding to @RonBeyer's comment above, among the first things you learn when you start flying is to make coordinated turns. In a coordinated turn, the gravity vector points perpendicular to the wings, even though the wings aren't level with the horizon. At that point, a simple sensor won't tell you anything useful; you'll need some kind of inertial reference, typically some kind of gyroscope.

@user3528438 ...or three things.

This video shows why a phone's "gravity" sensor or compass in water won't work https://www.youtube.com/watch?v=V9pvG_ZSnCc

well aware of the fundamental forces of flight. Idevice as simple as a cell phone though has enough accelerometer Hardware that it could probably act as a fairly accurate inertial reference device with the right app, and that would be immune to slip skid or other such aberrations.I know commercials have inertial navigation units but I've never heard of those being used to determine attitude... But I don't see why they couldn't.

as for the ground track, with small planes, maybe, but a commercial jet traveling at 600 miles an hour will still be traveling fairly close to that when measured at Ground speed, even with a 50 knot headwinds. if they are supposed to be going 600 miles an hour but are indicating 50 knots ground speed, I think that would raise some red flags about a stall.

In the cockpit of every plane I am aware of, there is a compass somewhere. It is the simplest form of a magnetic compass, similar to the "compass in water" you described. Due to physics, a compass will lead or lag when an aircraft turns, therefore it is very difficult to achieve a precise heading. But you can use it to point the aircraft in the general direction (within 10~20 degrees I'd say), and that is very helpful when nothing in your cockpit works.
Also, note that the vacuum pump does not require electricity to operate. For this reason, the Horizontal Situation Indicator (HSI) and the Turn Coordinator are usually powered by different sources. Both need a spinning gyroscope to function. One is powered electrically and the other by vacuum. This is intentional: in the event of either a total electric failure or vacuum pump failure, the remaining instrument can provide turn information. Only when you have a failure of both systems (exceptionally rare), will you loose all turn information.
By the same reason, the primary Attitude Indicator is vacuum powered and the backup Attitude Indicator is electrically powered.
The widespread of tablet devices has led to applications which serve as backup instruments as well. The application is not certified by aviation authorities to replace the on board instruments (at the time); however, more than one pilot has claimed that it saved his life by providing crucial situation awareness during an electric failure.
In an advanced aircraft, such as airliners, the systems are not only redundant, but also designed such that a single problem would not affect both systems. For example, the control cables on the captain side and copilot side are routed differently, making a complete failure extremely unlikely.

Voting to close because this question has become a rolling disaster on wheels. NO, a cell phone does NOT have enough sensors to double as an AHRS nor an IRU/INS. Nor does your toy wet compass.
The whole concept of “failure-proof” is pretty loopy... anything much more complicated than a paperweight will have some failure mode. Wet compass: freeze, crack & lose fluid, interference by some large metallic object sitting where it doesn’t belong, etc. Cell phones as failure-proof? Laughable as soon as you say that out loud.
No, I really don’t think that the industry that has turned flying through the stratosphere in a metal tube into the safest activity know to recorded history, has overlooked your phone & toy compass as ways to make things safer.

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Are there helicopters with vertically mounted turbines?
On the helicopter representation in this answer, the turbine is horizontal, with gear required to drive the vertical-axis propeller.

Are there helicopters where the turbine is vertical and directly driving the propeller, without gear? What are the advantages and drawbacks, or why isn't it possible if so?

Welcome to Av.SE!

@RalphJ Thanks! I will wait a bit before accepting one, but there are already pretty good answers

@Eth. There does appear to be  at least 1 helicopter with an engine mounted vertically. The Bell 207 Sioux Scout: https://en.m.wikipedia.org/wiki/Bell_207_Sioux_Scout. But .... it has a piston engine, not a turbine. See picture of the engine installation here:https://goo.gl/images/BGVtsq

@Eth.  The Bell H13, and 47, used in "MASH", also had a vertically mounted Franklin or Lycoming pistion engine, stated here: https://en.m.wikipedia.org/wiki/Bell_47

No gearbox, assuming the rotors could be driven at nominal turbine speeds, would mean a typical helicopter propeller's tips would have instantaneous linear velocity on the order of around mach 30 and would apply something like 120 tons of centrifugal force to the rotor shaft.  Clearly this won't work...

No a turboshaft cannot directly drive the rotor without a reduction gear, the rotor torque is too high for the ungeared turbine torque. The rotor blades are much longer than those of a prop or fan (relatively) and the rotor turns slower, a definite case for torque gearing.
Mounting the engine vertically saves a 90 deg gearing assembly, but places the engine where the payload is. Not good.

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What is the minimum size of a ramjet?
Having recently learned that 155 mm ramjet artillery shells are now a thing, I wonder how much ramjet engines can be miniaturized. Could we see ramjet tank shells? Man-portable recoilless guns? Shotgun shells? Rifle bullets? For less martial applications, could we see micro-ramjet engines for small drones, similarly to micro-jet engines? (Whether or not it would actually sell if built is out of the scope of the question, let's simply imagine that there is a market for ramjet-powered microdrones.)
Given current (or near-future) manufacturing techniques, what would be the limiting factor for ramjet miniaturization? What would be the performances for the smallest engines, and how difficult/expensive would it be to make them? Are there theoretical physical limits to the minimal size of a ramjet engine?
Note: this ramjet-assisted shell is probably using solid fuel, but limitations for liquid fueled ramjet specifically are also relevant.

Ramjets could be miniaturized, but at some point, air viscosity and boundary layer thickness will make it impossible for them to work. Simply put, the intake hole will get so small that air will find it easier to flow around the whole thing and ignore all of its complicated inner structure.
In more technical terms, as the intake shrinks, intake velocity will approach an asymptotic limit regardless of flight velocity due to boundary layer friction, and for very small intakes, the air mass flow will be insufficient to sustain fuel combustion. That point seems to be somewhere in the centimeter range, but an engine becomes increasingly less useful as it approaches this point. Manufacturing parts this size isn't a problem even now.
Ramjet shells can help long-range artillery, but ramjet tank shells would not be effective in combat.
The figure of merit for tank rounds is their high-density penetrator's sectional energy at the target. Discarded sabot rounds are more effective at delivering this than any kind of engine internal to the projectile. Combat ranges are short enough to preserve the velocity.
If you had to use some sort of engine for a tank projectile, it would be a rocket. The reason is easiest to explain in numbers. At a range of 7.5 km with average 1.5 km/s velocity and a 10 kg round, to get 500 m/s of delta-V, you need 10 g = 1 kN of thrust (engine), plus 50 seconds of impulse (fuel). We'll ignore engine mass for the first approximation.
A rocket with TWR=50 and ISP=250 seconds will weigh 100 kg / 50 = 2 kg for the engine + 10 kg * 50/250 = 2 kg for the fuel, for 4 kg total.
A ramjet with TWR=5 and ISP=1000 seconds will weigh 100/5 = 20 kg for the engine + 10 kg * 50/1000 = 0.5 kg for the fuel, for 20.5 kg total.
Simply put, when flight time is this short, a heavy engine like a ramjet doesn't pay for the minute amount of fuel (or rather oxidizer) mass it saves vs a light and powerful rocket.
This applies to all combat applications within visual range: rockets are better, and guns are better still if you can afford the launcher weight. Beyond visual range, rockets or hybrid gun/rockets take over, and past 100 miles, air-breathing engines become viable.

Back in the 1980's I saw a small ram jet from the 1950's to be used in model boats, planes and cars.  (1.25-2" diameter and 16-20" length.)  The accompanying literature suggested using a baby food jar as a fuel tank.  It used gasoline.  I expect anything today would utilize a bit more sophisticated (and safer) positive control of the fuel.  It was considered at that time to be the most powerful jet engine with the highest weight to thrust ratio in the world.  It was very light weight since it was essentially an empty tube with a small compression head.  Ramjets, despite some of their shortcomings, appear to be an economical alternative to complex turbine engines.  The MIG-21 was an awesome aircraft which was essentially an engine with a seat strapped to it.
I think it would be fairly easy for someone with a few engineering tools to make a small ramjet.  Expect to use double hearing and eye protection and devote a lot of fine tuning time as it will likely be a labor of love.  Your neighbors will not like it.

Well, physical lab-size prototypes, based upon a variety of factors, would suggest 40mm, perhaps 18.5mm (12 gauge) as a practical testbed minimum bore diameter. There has also been some 50/12.7mm work, perhaps smaller if the gyrojet is considered.
Theoretical limits are speculative, because designs would vary. There are atom stacked electric motors.
External projectile scram power presents itself as a variation on a theme for smaller bore projectiles, using the projectile itself as the solid fuel. Like a self destruct mechanism, it dissolves down range.
Powered vehicles get into the size/payload/altitude/range issue very quickly, along with acceleration and thermal survival of payload at ram/scram velocities.
50 year time-frame? Centimeters and grams.
22nd century? Molecular.
Best guess.

Welcome to Av.SE. Can you cite a source for any of this? Without something authoritative, the answer boils down to, "some anonymous somebody on the internet said..." and that isn't too useful as an answer.

Have you ever seen a photo or drawing of a Gyrojet round?  It's a rocket, not a ramjet...

I have about 12 years of r&d engineering on advanced weapons systems. I have more than forty in aviation. Not an expert, but a rki. Pictures? Grow up. Gyrojets have attributes that are part of the variables for mini powered vehicles. As with ram jets, there are many flavors and variations known, several still under wraps. Citations are always dated, limited, or advertising for some failed boondoggle by a mic. I didn't want to submit a white paper, just offer a little insight. This subject is extraordinarily complex.

This answer is nonsense and doesn't address the question that was asked.


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Which airlines did use a HUD for their A380?
Which airlines did (or still do) use a HUD for their A380 ?

According to this SNPL bulletin from 2015 (French airline pilots union):

Asiana and Korean A380 have a single HUD,
Air France and Qatar A380 have a dual HUD.

In addition Qatar wanted all their planes to be equipped with HUD in the mid-term.
Planes still flying:

Asiana: 5 flying and 1 parked
Korean: 5 flying and 5 parked
Air France: None since 2020 (had 10 aircraft)
Quatar: 8 flying and 2 parked

(according to Planespotters.net.)
Interestingly, China airports authority requires domestic airlines to have a quota of HUD-equipped aircraft (now 50%, 100% in 2025) in order to speed up airport operations, specially in low visibility. The HUD will need to integrate the image from an infrared camera fixed on the nose.

I wonder how the China requirement would have affected the A380. HUD allows aircraft without autoland to land in CAT IIIa conditions, but that would be a moot point for A380 which already has autoland. Maybe in China they have different RVR minimums for HUD? Or maybe the Thales article didn't apply to the A380.

My guess is the IR sensor mostly help detect heat from the approach and centerline lights in fog. It can help the pilot to decide to abort a landing, e.g. if the projected touchdown point is not safe. (It could affect China if one of its airline buys a A380 from a foreign company.)

I'm just wondering if regulations in China have different minimums or RVR requirements for fail operational autoland with HUD vs fail operational autoland without HUD. Could be, but if not then it doesn't seem like it would affect the number of A380 landings. Of course that doesn't stop them from making it a requirement for all planes. Makes things safer anyway.


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Can you drop the bombs of an F-16 during 9G-forces?
An F-16 simulator instructor told me that it is not possible to drop the bombs of an F-16 during 9 G-forces. I was surprised by this fact and looked it up, but I couldn't find anything about this. So I was wondering if this is true and why is that the case? Is this a safety issue?

It might be mechanical.  In other words, 9G might tear something before it had a chance to completely release.  Also, 9G might become alot more momentarily from weight loss, which could overstress the plane and be dangerous to the pilot.  Aircraft have been known to "toss" bombs while turning, so limits will vary.

That is not a blanket truthfullness.
"Bombs" range all the way from a 25LB BDU-33 practice munition, to a 2,500LB GBU-15. Different limits may apply.
Generally speaking, with large bombs and/or fuel tanks loaded, the jet is limited to 5.5-6.5G. The FLCC (Flight Control Computer and SMS (Stores Management System) work in conjunction to control this. This can be overridden by the pilot.
Also, "9G" is variable. A flat turn is different than a dive and pull up. Or, a "9G" turn, but you're already mostly inverted. Is the munition going to release cleanly and on target?
But if you're in a situation where you need to be pulling a 9G turn, you would have ejected the munitions anyway. The thing would wallow like a whale otherwise.
Fun off-topic factoid: The F-16A/B flight and design parameters are closer to the P-51 than to the F-35.

Not likely as the pylons capable of carrying bombs, i.e. stations 3, 4, 6 and 7 are load limited to 7.5 Gs.  Push beyond that and you risk structural damage with an air-to-ground loadout.  It’s also possible that the fire control computer does not offer computations for weapons release beyond those load factors as well. And it would be pretty hard to get off an accurate shot using a freefall dumb bomb, straining hard like that.

When I worked in munition development, the highest load at release that we tested was 4g - all on the F-16. That was about 40+ inert weapon releases and about 2 dozen live weapons. The SEEK EAGLE program office (who certifies a/c+weapon loadout and safe separation) used the test data and their aero models to set the ultimate limits that were put in the software.  And to your last comment, using continuously computed release point (CCRP) mode, the the FCC will release it quite accurately with no issue if you're within limits.


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Is it possible to fly around the world to stay in daylight with a fighter jet?
I was wondering if it is possible for a fighter jet to fly around the world and stay in daylight? For the Southern and Northern Hemisphere, the time and speed of daylight is different during seasons. So if not at the equator, would it be possible at the Hemisphere with different seasons?

What's your exact definition of "fly around the world"? You could fly in a very small circle around one of the poles to cross every longitude in just a few seconds, but I wouldn't really call it around the world.

Why specifically a fighter jet? Some specialised aircraft like Air Force One are designed to handle this for 50h straight, when refuelled in the air.

Can you clarify whether the Question assumes "… fly around the world… " to be on a great circle? To me it should, but several Comments here seem to suggest spinning on one foot round either pole would fit the bill…

Even near the equinox, when the day length is essentially the same over the entire world, this is possible.
At the equator, not so much; you'd have to average around Mach 1.5, including slowdowns for aerial refueling, to "make the sun stand still", though if you start at dawn and only need to get back by dusk, you gain another 12(ish) hours -- which, however, would still require an average speed of about 1000 km/h.  Possible, but having aerial tankers in the right places at the right times, over potentially hostile territory complicates things, not to mention the greatly extended flight path needed to avoid overflying places that don't permit it pushing the required average speed back up to the 1300 km/h range.
But if you fly far enough north or south, you could do this in a Cessna, providing only that you could somehow carry twenty-four hours of fuel.  Seems kind of like cheating, like those grade school riddles where you walk an hour south, an hour west, and an hour north and return to your starting point.
But in a fighter jet, with aerial refueling over the South Atlantic and South Pacific, you could circumnavigate at around the 45th parallel without having to overfly anywhere too hostile -- and given 36 hours to fly, only need to average around 600 km/h, which is well below "jet fighter" speed.

Better be a 2-seat fighter, if you plan to stay up for 36 hours straight! For 12 hours, with enough waivers (and help from the flight surgeon), you might could do it single-seat (i.e. an F-22). I think that & a lot of work by the diplomats may be the best bet.

Note that the standard definition of ‘circumnavigation’ requires crossing the equator twice.

If you fly far enough north or south, why fly at all?

The 'standard definition' requires you be in a boat.... And it's generally accepted that you'll have to cross the Prime Meridian, or any other longitudinal line, twice.

The category of "hostile" nations will naturally depend on the aircraft's nationality, of course - raising the associated question of which country's air force is best placed to achieve this...

If you were to include orbiting spacecraft, it might be possible at the equator.  The ISS is too high, completing an orbit in ~90 min.  There must be some ideal height between that and typical fighter jet height that would work?

@DarrelHoffman Actually, ISS is too low -- higher orbits have longer periods.  But in fact, you can't hover above the day side until you get all the way to the Sun-Earth L1 point, where at least one solar weather observation satellite sits -- and that's close to a million miles out.

@ZeissIkon Ah, right, I was just thinking - ISS is too fast, planes are too slow (or at least, the ones that are fast enough don't have sufficient range), so there must be something in between that would work?

Actually, aside from hostile airspace, an SR-71 could do this on the equator (they'd have to throttle back a little, though).  Maintain Mach 2 cruise at 70,000+ ASL and come down a few times to refuel.

@JanHudec by your definition (crossing the equator twice), that would be a pole-to-pole circumnavigation (vertical), most people would think of a horizontal (east to west or vice-versa) circumnavigation, no?

Any Great Circle that's not over the equator will cross the equator twice.

@FreeMan it can be nearly ‘vertical’ and count—you still have to cross all meridians. But you don't have to go near both poles, which is how you get the shortest route that would count—closely around the pole one one side to just past the equator on the other.

@TobySpeight The list of countries with sufficiently fast jets and enough tankers to support an attempt like this is rather short, and for China (and all the other equatorial / near-equatorial countries) countries to permit that much access to their airspace would be quite the diplomatic feat.  When you consider who could do this, saying that China is "hostile" to them, while maybe a slight hyperbole, isn't really wrong.

China is rather far away from the equator, approximately 1000 nautical miles. So that airspace wouldn't be an issue. There are actually surprisingly few countries along the equator that you would have to coordinate with, and quite a few of those would likely not be capable of intercepting a supersonic aircraft.

You can stay in perpetual daylight with a regular jetliner.

During northern summer, you operate out of Iceland. You take off in the evening, circumnavigate the north pole and land back in Iceland in the morning. The trip is only 5000km, but you have to stretch it up to 12h depending on season.
During northern winter, you operate out of New Zealand and circumnavigate the south pole every night, a trip of 8000km. You also have to stretch it up to 12h depending on season.
On spring equinox, you fly from New Zealand to Iceland, a distance of 17700km along the westbound route (AKL-NRT-KEF). You have 12h from sunrise to sunset and you gain another 13h time shift by flying west. 17700km in 25h is easily doable, even with a fuel stop.
On fall equinox, you fly from Iceland to New Zealand, a distance of 16800km along the westbound route (KEF-AKL). You have 12h from sunrise to sunset and you gain another 11h time shift by flying west. 16800km in 23h is easily doable, even with a fuel stop along the way.

A jet fighter is ill suited for this mission, it lacks range and endurance. Use a random jetliner with >12h endurance and >9000km range.

Nice alternate thinking!

Why do you get extra time flying eastbound?

If one had a pair of bases in Alaska and Iceland, and another in New Zealand and Chile, I would think one could greatly reduce the required flight times during Northern and Southern summers, if the plane set out from each base each evening, landed at the other base in the morning or afternoon, and could then refuel and wait until that evening before setting out for the first base.

@supercat - I don't think that will help. Iceland-Alaska-Iceland is about 11000km or 12h flight time. Iceland-Pole-Iceland is a lot shorter and you can return to Iceland after less than 12h usually (nights in Iceland are rather short around midsummer). Only close to the equinoxes you have to loiter at the pole and wait for sunrise in Iceland.

@RainerP.: Punching values into a great circle calculator, I get a distance of 4,472km between 71N156W (Wiley Post–Will Rogers Memorial Airport) and 66N18W (Grímsey Airport).  How were you figuring the 11000km distance?

I just realized, the great-circle route won't work near the equinox, but flying Iceland-Pole-Alaska would be slightly shorter than Iceland-Pole-iceland (since Alaska's airport is further north), and would allow a worst-case time airborne of about 8 hours instead of 12.

@RainerP.: My strategy would require flying a greater total distance than yours, but is designed to minimize the worst-case requirements for the aircraft.

@supercat - I took the Keflavik-Fairbanks-Pole-Keflavik round trip for reference, which is 10750km. That trip takes the entire night (12h worst case) anyway, so you can skip the stop in Fairbanks.

@RainerP.: From what I understand, commercial flights would need to stay within two or three hours of a usable emergency landing location, but I don't think any kind of flight to the North Pole could satisfy that criterion.

@RainerP.: BTW, I don't think it's necessary to wait for equinoxes if one exploits the fact that for any two points that are exactly opposite each other on the globe, sunrise at one  will coincide with sunset at the other, regardless of the season.

@RainerP.: Thus, if one takes off at sunrise from e.g. 60N0W and can flies a great circle southwest to 60S180W in just under 24 hours, one will arrive just before sunset, whether sunrise was 9am and sunset was 9pm, sunrise was 3am and sunset at 3pm, or anywhere in between.

If you use the FAI definition for setting round the world speed records the rule states a trip minimum of 22,847 miles and all longitude lines must be crossed below 66deg latitude. If you start at sunrise on the longest day of the year at 66deg you get 24hr for a full day plus 20hr of daylight to sundown, or 44hr.
22,847mi/44hr is 519mph ground speed. If you can avoid head winds this is doable in private jets, as well as commercial and military jets. You may not even need to refuel in the air if you have extra tankage.

Doesn't the jet stream go west to east and you need to fly east to west? That would be a 100 mph head wind. Also you switched latitude and longitude in your description.

If you time this correctly, starting just past dawn near the equinox, then you have 24+12 = 36 hours.
This is less of a problem than other answers suggest. The around the world (crossing the equator) record is currently held by a Concorde flight with a time of ~33 hours, which is easily fast enough. I can't find exact times for every stop, but I think they may have stayed in daylight the whole way based on start/end times. Also they were supposedly only airborne for ~25 hours, maybe the Concorde is quite slow to refuel? But that is good if you only care about yourself and not the plane, as probably having a bunch of Concordes and switching planes instead of refueling would cut off several hours.
(Per Bianfable in comments, this is not so much the time spent at each individual refueling stop but the number of refueling stops--so you will need quite a few Concordes to really get to that minimum time. If my math is right you can theoretically get the minimum time with only four Concordes, but that also requires some of them to fly multiple legs, i.e. they would fly an early leg and then turn around and fly the other direction to meet you for a later leg....)
This is poorly documented, but what little documentation I'm finding suggests that the previous record for this was a hair over 36 hours in a Gulf Stream which is also very nearly fast enough, just in case you don't have a Concorde to hand. (It makes sense that a Gulf Stream or other business jet would be good for this, since they are basically for rich people who want to get places in a hurry without having to stop too much along the way.)

On supersonic flights Concorde can only stay in the air for 3½ to 4 hours. It'll burn about 80 t of fuel in that time, so refueling will take quite a while. 25 h airborne for 33 h total time seem reasonable to me.

It is important to note though that the Concorde cruised a lot faster than any fighter jet (only SR-71 cruised faster but that is not a fighter). Most fighter jets don't cruise supersonic at all (supersonic flight requires continuous afterburner, which uses too much fuel for long flight) and the best is around Mach 1.2. Compared to Concorde around Mach 2.

@JanHudec apparently the best is around Mach 1.5: https://en.wikipedia.org/wiki/Supercruise#Military_use


text:
Why are the wheels of aircraft relatively small?
I was wondering why the wheels of aircraft are relatively small compared to for example cars? I could imagine that it is more efficient when traveling to have smaller wheels. The majority of commercial plane tires are only 27 inches in diameter and smaller aircraft have tires at 15 inches [1]. The wheels of standard road cars are between 14 and 19 inches in diameter [2].

Sources:

Executive Flyers [1]
Tiger wheel&Tyre [2]

Closely related https://aviation.stackexchange.com/q/91559/60886

Hmmm.  You quote cars at 14-19 and planes at 15-27.  That’s a lot of overlap with plane tires being bigger.   And then there’s the “40s” on some bush planes

One of the reasons for large diameter tires is for rolling over bumps and obstacles.  Planes (other than bush planes) don’t have a need for that.

A more interesting question is why cars have big wheels and trucks and buses have even bigger wheels. It’s also interesting how tiny the wheels of some trailers are (which kind of shows that it’s possible to have small wheels, just not optimal).

It depends on their purpose. Aircraft which have to land on rough terrain happen to have huge wheels: https://www.pinterest.com/pin/595601119461493175/

As usual in the aerospace world, it is a compromise among contrasting requirements.
Wheels must be big to pack enough disks for the (disk) brakes. But they must be as small as possible too, in order to minimise weight, drag, needed space for stowing and inertia when they suddenly start to rotate upon touchdown.

Same for cars, actually - the rims are as small as possible, but the brakes must fit. Some people like ridiculous-looking large rims with tiny brakes inside, though... like putting 20 inch rims on a tiny 200hp diesel

Also the wheels are unused for almost the entire flight.  Unless they are touching the ground they are just taking up space and weight, so there are strong incentives to make them a small as possible.  They also need to be quite strong, so something like bicycle wheels would be unsuitable.

@Frog tell that to the Wright brothers.

The inertia point is good for tire wear on landing.  Maybe strong light spoked wheels might not be a bad idea after all.

@Haukinger Note that airplanes get around the brake diameter issue by using a stack of multiple discs and friction materials... they are very similar to automatic transmission clutch packs and motorcycle clutches rather than car disc brakes. This shows the different design trade-offs: cooling is awful relative to cars, but in normal use, you have at least an hour between major uses. For the dimensioning case (rejected takeoff), the brakes may very well be destroyed in one stop, or at the very least, have to sit and cool for 3+ hours.

@user71659 exactly, also airplanes can just add more wheels if they need more braking power. And regarding cooling, you have a fire truck ready and waiting each time you actually use the brake, if you're a plane :D

@MarkRansom All of the Wright Flyers used skids.

And even the later Wright aircraft that did have wheels, also had skids in combination with the wheels.

@Davidw I did not know that, thanks.  Just assumed since they were bicycle makers they would have used bicycle wheels.  Probably would have taken me 2 seconds to find an online image before I opened my mouth.

@RobertDiGiovanni: "Maybe strong light spoked wheels might not be a bad idea after all". It might be a bit difficult to put spokes on a wheels like this :)

Car wheels have an entirely additional job besides supporting the chassis that aircraft don't: transfer engine power into motion.
Aircraft have only one: converting rotation into heat. Other than during deceleration the wheels spin freely. Whereas on a car larger wheels mean lower speeds in the transmission, gearbox and ultimately crankshaft. (You can try this by changing the size of the wheels on your vehicle and observing how the speedometer now needs to be recalibrated)
Brakes themselves are pretty good and don't dictate the size of wheels once you cross a certain threshold.
Another key factor in wheel size is ground clearance. The axle is often the lowest clearance on many vehicles (suspension lifts are popular in off-roading world which is slightly bizarre given it does nothing to change the minimum ground clearance unless the sump or gearbox already hangs below the axles). This isn't really a concern in aviation, in part due to the fact there aren't axles connecting e.g. left and right main gear, the wheels in each set function almost like a single wheel in terms of ground clearance. (and the clearance is really there for the engines rather than particularly rough terrain)
So it's not just a case of compromising on requirements between use cases - some of those requirements don't even exist in both cases.

On an off-road vehicle, the wheels will lift the axle over most obstacles.  The body gets no such lift.  Yes, a lifted suspension gives no advantage for rocks in the middle of the track, but for other obstacles such as logs or ledges, it greatly increases capabilities.


text:
History of Epilepsy- want to apply for medical
I have a history of epilepsy when I was in high school/first 2 years of college due to a few brain surgeries I had as an infant. I still take medication for them. I know this sounds like an automatic DQ. But I have not had a seizure in a few years and have had multiple brain scans that show normal brain activity since my last episode. Could this possibly be used as evidence for being medically fit to fly?

You have to ask a medical examiner that question. Nobody here can answer it. Even if someone here says maybe possibly, you still have to go see an aviation examiner.

I’m voting to close this question because it's only answerable by an aviation medical examiner with full access to medical records and tests.

Different question, but this answer (talk to an AME) applies: https://aviation.stackexchange.com/a/27346/7532

Schedule a CONSULT with an Aviation Medical Examiner and see what he/she says. Do NOT go in for a regular FAA airmen's physical. If you've ever been denied a medical certificate, you cannot fly a light sport aircraft (that doesn't require an FAA medical certificate). If your consult looks like you could never get (or not likely get) an FAA medical certificate, you could still fly LSA if you chose.

@RetiredATC 14 CFR 61.23 (c)(2)(iv) "Not know or have reason to know of any medical condition that would make that person unable to operate a light-sport aircraft in a safe manner." Pretty sure known history of epilepsy would fall under that.

@Ron Beyer There are certainly medical conditions that would indicate a person shouldn't operate an LSA aircraft. Does the OP have one? I don't know. I don't know how long it has been since his last event. I don't know what medicine he is on. I also don't know if he has been issued a driver's license from his state. Those are factors (and probably others) one would have to take into consideration prior to beginning LSA flight. My advice was to make sure the OP knew that if he/she were denied a medical certificate LSA flight would not be a possibility.

I've voted to keep this question open. It is not strictly per norms here, but has huge educational value IMO.

NO. Epilectics are not allowed to be licensed pilots under very explicit FAA rules. There is more or less zero chance you can get a medical of any type if you disclose your condition.

Obviously the answer here depends on consultation with your AME.  However, there are some incredibly useful resources from the FAA for each and every disqualifying condition.  I highly recommend you review these resources, and then discuss them with your primary care physician first, and then consult with an AME.  All of these links are to FAA sources:

Here is the questionnaire that you will actually review with the AME, so you can print it right now and review it first with yourself, and then with your physician or psychiatrist before proceeding to an AME.

FAA Psychiatric and Psychological Evaluation Specification or the similar FAA Psychological Evaluation Specification

Consider contacting an AME who is part of the HIMS program, they are designated to help people with mental health issues assess their eligibility.

For all conditions, the FAA publishes guides that inform both the pilot and the AME about the specific criteria that can lead to issuance, AME Assisted Special Issuance (AASI), disqualification, etc.
Always research your particular condition starting with this FAA page before deciding whether or not to proceed further.

Please add a warning not to apply in MedXpress until the AME has confirmed OP will pass.  Until then, they should only schedule consultations (not exams) to avoid disqualifying themself from Sport.

Well, since you specifically ask "Could this possibly be used as evidence for being medically fit to fly?" I will offer the obvious answer yes, it can be offered as evidence.
This site, even with all the wisdom and knowledge gathered together, cannot answer the question whether or not that evidence will be considered valid by AME.
Most importantly you should ask yourself whether you honestly consider yourself fit to fly? Having a medical condition such as epilepsy has, unfortunately,  great potential to put you and other people in great danger. An epileptic seizure while flying solo will almost certainly lead to at least one fatality.
I've offered myself as an example in these kind of questions popping up here. I fully understand the keen interest in aviation as a hobby (and often as a profession too). It is pretty much the most exiting thing one can do with clothes on. As such it sometimes may blur ones judgement. My judgement was blurred in the sense that I have a medical condition that as such will automatically prevent me from obtaining a medical, but I was "fine" for years and years. I was able to get medical statements that convinced AME to grant me a medical and up in the air I was. Untill, luckily while on ground, I had two consecutive medical events in short succesion. I considered myself lucky, and quite happily grounded myself and have not flown since. It may be exiting, but not worth dying for.
Airplanes, especially smaller ones are physiologically (and psychologically) more or less hostile environments. There is a lot of physical stimuli and sensory load present all the time, and should one be susceptible to adverse medical events, the risk of that happening is greatly elevated while flying.

The information listed here is great but I think there is one important missing piece, you note:

I still take medication for them.

If you look at the FAA's Do Not Issue/Do Not Fly list here it specifically calls out:

Seizure medications, even if used for non-seizure conditions such as migraines

and later on (bolded for emphasis)

Do Not Fly. Airmen should not fly while using any of the medications
in the Do Not Issue section above or while using any of the
medications or classes/groups of medications listed below without an
acceptable wait time after the last dose. All of these medications may
cause sedation (drowsiness) and impair cognitive function, seriously
degrading pilot performance. This impairment can occur even when the
individual feels alert and is apparently functioning normally - in
other words, the airman can be "unaware of impair."

In the eyes of the FAA its not only about controlling the issue but in some cases having it controlled and being medication free.
As always, you should seek the advice of an AME as they are the only actual authority on this matter.


text:
Why would passengers be required to close window shades when passing Ukraine
Last week, my friend flew from Europe to Japan, passing Ukraine to the south along the southern coast of Black Sea. When nearing the Black Sea area, the passengers were required to draw the shades on all cabin windows. The daytime was drawing to and end at this point.
Do you know of any reason relating to the war in Ukraine that would cause an airline to issue such a demand or is this rather just the standard procedure of darkening the cabin for the night during an eastbound flight?
The main reason we started to wonder about this is that dinner would still be served after issuing the command so it was not like majority of the passengers would be looking to sleep just yet. Personally I am skeptical that the passengers would be able to see explosions, missile trails or other alarming phenomena from the other side of the sea.

it's normal for long distance flights to have passengers to close the shades in the cruise portion of the flight to facilitate sleep. closing them before serving dinner is not unheard of for me, as you say "The daytime was drawing to and end at this point"


text:
In Virginia, can a crop dusting/seeding operation refuel and re-supply on agricultural property that they are working?
It has been reported that a crop dusting/seeding operator is refueling and re-supplying his plane on agricultural property that he is working. Just trying to make sure this operator is operating within any regulations set forth for crop dusting/seeding operations.

As in, landing on a runway that's part of / owned by the same farm that he's applying (whatever) to? Is that the scenario you're asking about?

Ralph, yes, the pilot is landing on the property owned by the same farm that he is applying seeding.

Note that there may be additional state/county laws for such operations, which are not covered by FAA regulations. You may have to ask on Law.SE regarding those laws.

If the runway would be legal to land on generally, there shouldn't be anything about applying seed to the same owner's other fields that makes it off-limits. All the rules that apply everywhere else (permission required, handling of chemicals, etc) would still apply, but I don't think that same-ownership would create any particular barrier to using that particular runway for resupplying to seed those particular fields.

What is the nature of the reports?  i.e. neighbors complaining about noise, or environmental or safety concerns around off-airport refueling operations?  Because that drives different answers.

I think it is a combination of noise of the operation, and the safety and environmental concerns associated with refueling and re-supplying in an agricultural field. I believe this  individual may live within sight of the farm and saw what was going on and then expressed his concern.

Well, ground based tractors also make noise, spray chemicals, and need to be refueled.  My first impression is that there's nothing abnormal or illegal about this as long as it is done on private property.  (Complainers will complain, and aviation seems to draw a disproportionate number of them...)

It seems like you are broadly asking "is it legal to land in a random field" the broad answer is, yes generally you need the owners permission and so long as there is no local ordinance preventing it you can land, refuel, resupply and do what you need in a field. You can find more info in these question

What procedures are followed for a planned landing in a field?
When it comes to private airports those marked on sectionals with (Pvt) what frequency's do they use if any at all
How are unpaved strips created and maintained?
What are the FAA regulations on grass airstrips?

Broadly, maybe... I didn't interpret the question as being about landing though.  As Ralph mentioned in a comment above, I think there's more risk in violating some obscure fuel and chemical handling regulation, and that was really how the question was worded.

@MichaelHall I read the question as focusing on the fact that the same owner owns both the landing strip and the field being worked -- which I don't think adds any limitation to the operation. Regardless of the ownership, all the fuel/chemical handling regs (federal/state/local) apply, and rules about where you can/can't land apply. But those all apply no more & no less in the case of same-owner than they would if the landing was on somebody else's property. "On property that he is working" doesn't make things less permissive, but there's plenty of rules to be met, regardless.

@RalphJ, I read it that farmer owns the land too...  In summary:  Farmer pays crop duster to dust crops, plane lands in farmers field to refuel and replenish, is the the refueling and replenishing legal?  (vs "is landing in the field legal"...)  Either way, I think the complaintents would accept any answer in favor of shutting it down.

"Either way, I think the complaintents would accept any answer in favor of shutting it down."  Agree!


text:
What coordinates do helicopters (preferably) use?
There are different ways of representing coordinates.

When I went to school, in geography class, we learned longitude and latitude as degrees, minutes, and seconds (like  52° 30' 59" N,  13° 22' 40" E)
When I copy a position from a maps app, I get decimal coordinates (like  52.51625 °N,  13.37767 °E)
In nautics, coordinates use decimal minutes (like  52° 31.0' N,  013° 22.7' E)
The institutions of disaster relief use UTMREF system (like 33U UU 8996 1970)

I am aware that you can convert all these systems into each other. But still:
I am particularly interested in the coordinate notation that is preferably used in helicopter flights. If this differs from region to region, I'm particularly interested in what's common in Germany.

Military or civilian?

Used in what context? User input in a system, internal representation of that system, ATC communications, else?

Use of a coordinate system is more dependent on mission and location than aircraft category and class.

In Canada actual aeronautic navigation is Lat long, but when flying for industry its normal to use UTM coordinates instead as they are simpler to relay and are more suited to the short distances and precision need to navigate to a particular clearing or tiny helipad.

The standard in aviation is same as Nautical. That is Degrees and Minutes, and if a position needs to be depicted more precisely than that, they don't use Seconds (60 in a minute) they use tenths of minutes.
So you will see "45o 30'N" for 45 degrees, 30 minutes, but for a more detailed locator, they just add a decimal to the minutes value, instead of seconds. Thus it becomes something like "45o 30.6'N" for 45 degrees, 30 minutes and 6 tenths of a minute.  The grid sub unit marks on aviation charts are in tenths of a minute as well.

In our institution, we operate a research helicopter based on the Eurocopter EC135 (now renamed to Airbus H135), the ACT/FHS.
As we develop control algorithm for this machine we use two formats:

Due to the digital output of our custom Inertial Navigation System, we use the decimal representation of the GPS coordinates (like 52.51625 °N, 13.37767 °E). This is the most convenient format, as we can use it digitally.
Often, for local navigation, we translate these coordinates to a local NED frame, which we then can use for a lot of local navigation algorithms. In this frame we can say that we are for example 500 m North, 200 m South and 300 m up from a given reference point. This is a lot easier to use, however if you are farther away then 30km from your reference point, the local approximation really starts to show.


text:
Is there a formula for calculating lift coefficient based on the NACA airfoil?
Are there any formulas that can be used to calculate this?

There are, but it quickly gets a lot more complex.  What are you really trying to do?  There are many NACA airfoil families, which are you interested in?  Two-dimensional characteristics of an airfoil only get you so far -- the switch to 3D gets much more complex and there are far fewer closed form solutions.

I'm interested in two dimensional NACA 4 digit airfoil

5-digit and 6 digit there are number telling their coefficient of lift, but not 4 digit. For the 5-digit: the 1st number multiplied by 3/2 then divided by 10, or 1st number multiplied by 0.15. For 6-digit: the 3rd number divided by 10. https://www.youtube.com/watch?v=y6D3qhss7vc

To my knowledge the 4-digit NACA airfoils have been specifically conceived during a project to systematically measure the effects of camber, thickness, etc. rather than just relying on "a formula" (thin airfloil theory or such). The results of are in NACA Report No. 460 (publicly accessible),  there the results are also compared to theoretical values.

Is there any reason you have not accepted my answer below?  Do you need any further clarification?

Thin airfoil theory can be used to calculate lift based on the shape of the mean camber line.  This involves some integrals, but these have been worked out ahead of time for certain camber line families like the 4-digit one you are interested in.
$c_l = 2 \pi \alpha + \pi (A_1-2 A_0)$
$A_0 = \frac{1}{\pi} \int_0^\pi \frac{dy}{dx} d\theta$
$A_1 = \frac{2}{\pi} \int_0^\pi \frac{dy}{dx} \cos(\theta) d\theta$
$\frac{dy}{dx}$ Is the slope of the camber line.
We use the transformation:
$x = \frac{1}{2} (1-\cos( \theta))$
These integrals have been worked out for a 4-digit mean camber line (Houghton and Carpenter, 4th Ed, pp. 252).
$A_0 = \frac{m}{\pi p^2} [(2 p - 1) \theta_p + \sin(\theta_p) ]\\ + \frac{m}{\pi (1-p)^2} [(2 p - 1)(\pi - \theta_p) - \sin(\theta_p) ]$
$A_1 = \frac{2 m}{\pi p^2} [(2 p - 1) \sin(\theta_p) + \frac{1}{4} \sin(2 \theta_p) + \frac{\theta_p}{2}]\\ - \frac{2 m}{\pi (1-p)^2} [(2 p - 1) \sin(\theta_p) + \frac{1}{4} \sin(2 \theta_p) - \frac{\pi - \theta_p}{2}]$
For a 4412, $m=0.04$ and $p=0.4$.  $\theta_p=\cos^{-1}(1-2*p)=1.3694$ radians.  $A_0 = 0.00811$ and $A_1 = 0.1632$.
Pulling it all together gives:
$c_l = 0.46175 + 2 \pi \alpha$
Finite thickness and viscous effects will reduce the true value a bit from this, but it is pretty good.  To do better than this, things get substantially more complex.

Where or how did you get this (CL = 0.512 + 2 * pi * alpha_rad) formula? As far as I know, the first digit is representing its maximum camber in chord line (C), i.e., 4% of its C, the second digit is representing its location of its maximum camber x 10%, i.e., 4x10x% of C, and the last two digits representing maximum thickness in regard to its C. Nothing about coefficient of lift.

I missed a term in my exposition above corresponding to the angle of attack for the design lift coefficient -- it is not zero.  I will edit my answer and also give a reference to a textbook with this example worked out.


text:
Is there a formula for calculating drag coefficient based on the 4 digit NACA airfoil?
Are there any existing formulas that can be used, or maybe some methods to derive an equation that can calculate the drag coefficient based on the NACA airfoil?


text:
Decluttering scenarios on 737 MAX navigation display
The 737 MAX FCOM mentions an 'EXCESS DATA' warning that shows on the navigation display when there is too much data selected to be displayed at a time.

For example, this applies when you attempt to select terrain and weather at the same time. However, I am not sure of when this message will occur in any other scenario. I imagine it would appear when too many waypoints/airports are available in the current view (the MAX navigation display has a maximum range of 640 nautical miles so it does not sound impossible to me). However, I'm not sure of the specific number that will show the message, or of any other criteria that may apply. Does anyone have more information on this?

Not quite.  Selecting Terrain de-selects the weather radar display, and vice versa.  Maybe a bad flight simulator throws up the "Excess Data" message when doing that, but that's not when you get the message in the actual aircraft.
The first three mentioned switches (STA = navaids, WPT = waypoint triangles, ARPT = airports) put "things" on your map display, and when you've put too many for the display to handle, that's when it displays the Excess Data message, and not everything you've asked for is visible.  This most often occurs when you have both navaids and airports turned on at some reasonable scale like 80 miles, and then you switch to a much larger scale, like 320 miles: now the map has far more area that it's displaying, and instead of a couple dozen objects (navaids and airports) to display, it has hundreds, which would clutter the screen and presumably degrade the ability of the map to redraw as it should. So instead it displays the error, and you either reduce the scale, turn off some of the options, or both, and the error goes away.
The map on the Max is really huge, and it seems like it has a much "smarter" ability to declutter by not displaying as many "things" in the same geographic area at the large scale as it does at a smaller scale.  The Next Gen aircraft do this to some extent (i.e. ILS DME stations are displayed on the small scales like 10 or 20 miles, but not at larger ones like 80+ miles), but the Max seems to be able to just declutter so that you aren't seeing overlapping objects, even when you're looking at most of the western US all at once on the map.


text:
Air quality monitoring devices for a320
I looking for the air quality monitoring devices for a320. How do they look, where they located?
thank you for the help

Your question presumes that such devices even exist.  Do you have any evidence that they do?

Far as I can tell, there are no passive or active air quality monitoring devices on the A320. The cabin air systems on modern airliners are designed against an air quality standard, and their performance is tested with equipment that is installed on the test aircraft for that specific purpose.
EASA published the results of an air quality campaign test program in 2017.

In total, 69 measurement flights were performed between July 2015 and
  June 2016 on 8 types of aeroplane/engine configurations. This included
  61 flights on aeroplanes equipped with engine bleed air systems, and 8
  flights on Boeing 787 which is equipped with electrical compressors
  (‘bleed free’ system). For all flights, measurement equipment was
  installed in the cockpit and in the cabin.
The results show that the cabin/cockpit air quality is similar or
  better than what is observed in normal indoor environments (offices,
  schools, kinder gardens or dwellings). No occupational exposure limits
  and guidelines were exceeded. Special attention was paid to
  organophosphates, in particular TCP (Tri Cresyl Phosphates) with the
  use of high sensitivity analysis techniques. Only traces of TCP meta-
  and para-isomers were sometime detected in all aeroplane types, but no
  ortho-isomers were detected.


text:
What is the "off-side engine generator" on an A320?
For the A320 family, is the "off-side engine generator" the same as the "emergency generator driven by the RAT"? I can't find the location of the "off-side engine generator" on the A320.

Neither the off-side and on-side engine generators are RAT generators. They are both just the generators attached to each engine. As far as I can tell, if there is a failure of one of the parallel electrical buses the off side is the failed side and the on side is the operating side.


text:
Flying on one engine
Can a commercial jet with two engines, fly on one. If so, what are the limitations. Maby some are better than others in this situation

Related: https://aviation.stackexchange.com/questions/21752/what-is-the-main-difference-between-an-etops-certified-and-non-etops-certified-p https://en.wikipedia.org/wiki/ETOPS


text:
Could DC-10s be equipped with seatback inflight entertainment screens, given that the oxygen systems are in seatbacks rather than overhead?
Unlike most passenger aircraft, the supplemental oxygen mask system on the McDonnell Douglas DC-10 was located in the backs of passenger seats, rather than in an overhead compartment in the passenger service unit.
However, this seems to me like it wouldn't be possible to equip DC-10 aircraft with seatback inflight entertainment screens, since there'd be no space in the seatback headrest to hold the required electronics for a display screen as it'd all be taken up by the oxygen system.
I've seen this video, which shows seatback screens on an MD-11, which I think is simply a stretched DC-10, and looking closely I think the supplemental oxygen is located in the standard spot, overhead in the passenger service unit. I think the position must have changed for the MD-11 aircraft.
Was it possible for airlines to equip the DC-10 with seatback IFE screens? Was there an option to have oxygen masks in the standard overhead spot? Or did no airline ever equip their DC-10 with seatback screens?

Given that the DC-10 has been out of passenger operations for over 7 years this question is moot, I would say that anything is possible with enough engineering. It would probably be far easier to just give people tablets and collect them at the end of the flight.

I’m reading this question on my iPad.  It is about the same size as a seat back screen, and roughly a quarter of an inch thick.  Do you think the seats could be made a quarter inch thicker if it was absolutely needed to accommodate both?  I don’t have an answer for you, but it is entirely believable that both might fit.

Have you seen how thin tablets and laptop screens are?  Why would you think they couldn’t be used as the flip-down covers shown in the video?

@Jim Modern tablets use LED backlights. But back when the DC-10 was in service and IFEs were installed, LED-backlit screens were super expensive, and that extra cost would add up when installing 200+ screens. As such most other aircraft types' IFEs used the much cheaper but thicker and heavier fluorescent light backlights. Also, you'd need quite a bit of cabling to connect the touchscreen to the IFE box under the seat. As such, I don't think it was viable to put IFEs in the seatbacks, though I could be wrong.

@MichaelHall See above.

@gparyani - I guess I misunderstood your question. It asks “Could DC-10s be equipped” not “Could DC-10 have been equipped”.  From that I assumed you meant today not back then.

@Jim Yeah, I meant "could" as the past tense of "can".

“Could have”, or the shortened “could’ve” (never “could of”…) is past tense for can.  “Could” alone is more aligned with “possible”.  But I got your point…

@GdD You should make this your answer. I think this one should be accepted as correct.


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Specific Squawk Codes Information
First time poster.
Can anyone tell me please what these 3 codes mean in simple language.
3462
2042
2747
Many thanks

Nothing
The only squawk codes that have meaning are 1200, 7000, 7700, 7600, 7500, 4000, 2000 and 1000 The other codes are simply assigned to aircraft for a given flight in a given sector.

Cheers and thanks

1201, 1202, 1205, 1206, 1234, 1277, 7777... there are a lot more codes with specific meaning, at least in the USA... https://www.faa.gov/regulations_policies/orders_notices/index.cfm/go/document.information/documentID/1040351

As @Dave pointed out, there are very few squawk codes which have the same meaning across all countries in the world. So at the very least we would need to know where in the world these codes were assigned.
If these codes were assigned in the usa, then I would say the following:
The codes you reference are in the 2000, 2700, and 3400 blocks. According to FAA JO 7110.66, National Beacon Code Allocation Plan, each one of those blocks is an "External ARTCC code block." In other words, these are code blocks which the Air Route Traffic Control Center computer draws from when assigning a code to an aircraft whose filed route will take it outside of that Center's airspace.
The NBCAP document includes a list of which blocks are assigned to which facility. For example, you can see that the 3400 block is used by ZAN (Anchorage Center), ZBW (Boston Center), ZFW (Fort Worth Center), and ZID (Indianapolis Center) for external departures; it is also used by ZJX (Jacksonville Center) for internal departures.
For the most part squawk codes are assigned randomly when necessary. But some facilities may take certain of their internal squawk codes and permanently assign them to specific "frequent flyer" aircraft that are based in the area, such as medevac helicopters or flight school trainers. So for example the code 0261 may be assigned to "Flight School 1" and 0262 may be assigned to "Flight School 2," and those codes have been removed from the pool that the computer draws on when assigning codes to other flights. These types of code assignments are unlikely to use the codes you asked about.

I did not know (until it came up in casual conversation with an ATC) that an aerobatic trainer based near my home airport had its own unique squawk code assigned which had all of the rate-of-climb/descent warnings disabled.


text:
Obtaining a special formula for the Theta-Beta-M diagram
I'm currently studying shockwaves, particularly their effects on drag.
I've stumbled upon an odd formula in "Elements of Gasdynamics" (Liepman and Roshko, pages 52-53), in there I saw an alternative formula for the theta-beta-mach diagram, and the author committed a passage in which I've been having problems replicating.
Starting from:
$
\frac{\tan (\beta - \theta )}{\tan(\beta)} = \frac {(\gamma-1) M_1^2 \sin^2(\beta)+2}{(\gamma+1)M_1^2\sin^2(\beta)}
$
He divides and multiplies right hand side by $\frac{1}{2} M_1^2 \sin^2(\beta)$
To obtain:
$\frac{1}{M_1^2 \sin^2(\beta) } = \frac{\gamma+1}{2}\frac{tan(\beta-\theta)}{\tan{\beta}}-\frac{\gamma-1}{2}$
Finally he ends up with: $M_1^2 \sin^2(\beta) -1 = \frac{\gamma+1}{2} M_1^2 \frac{\sin(\beta)\sin(\theta)}{\cos(\beta-\theta)}$
The last passage is not very clear and I have no idea how he ended up with that, I've tried with Wolfram and both equations are solved for the same* points, yet I am unable to find a way to obtain the latter.
My main question is if there is other literature where this formula appears, I liked it because it allows the introduction to linearized supersonic pretty easily rather than using the potential.
Needless to say I tried all the trigonometric tricks I could find.
Any help is appreciated, thanks.
PS: I consulted, Fundaments of AD, Elements of Aerodynamics of Supersonic Flows, aerodynamics for engineering students and Dyamics and Thermodynamics of compressible flows.

I pulled out my original edition of Liepmann and Roshko (c. 1957, 1965 printing) and found the equations above on pp. 87-88. Getting the second equation is easy enough, but I am stumped also on getting the 3rd.


text:
14 Part 121 Subpart U
14 Part 25 Subpart U states that it covers "Dispatching and Flight Release Rules". I am trying to understand why the FAA made a clear difference in using the words "dispatching" for Domestic and Flag rules versus "Flight Release" rules for Supplemental. It doesn't appear the FAA has loaded historical NPRMs for Part 121 on www.drs.gov so I can't read the FAA's reasoning or comments on why they wrote the subpart and rules (e.g., 121.591) this way years ago.
Why didn't the FAA just use "Dispatch" for all three operations?


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FMA alignment on A220
I have been doing some research on the A220, and one thing that has confused me is the alignment of the flight mode annunciator on the PFD. Take a look at the autothrottle mode on the far left of the FMA.

It looks like the engaged mode it right-aligned and the armed mode is center-aligned. However, this alignment changes apparently unpredictably when it goes to another mode, such as this:
Asimilar thing happens with the lateral modes, and the vertical mode looks all left-aligned, but with varying margins from the border of that section. Is there a reason why this works that way, or am I missing something basic?

Where are these screenshots coming from?  Are they from the actual aircraft in flight? A full motion simulator? A PC simulator? CBT lessons for the aircraft? Syllabus documents? Other sources?

All of these screenshots are from actual in-flight aircraft.

The A220 (nee Bombardier C Series) uses Rockwell Collins Proline Fusion. The character alignment will be detemined by the software code for the display (or maybe from the data  source). I suggest you send an email on your company's email platform and letterhead to RC tech support.
avionicssupport@collins.com

Well I am a hobbyist, not by any means in professional aviation, so this probably won't get me far. Thanks though.

@IsraelO.Emmanuel Ok I thought you were an A220 driver.  Hey, try it anyway. Can't hurt.


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How can I switch from MAG to TRU heading in a 737?
I was reading the section in the FCOM for the 737 MAX concerning the heading display on the bottom of the PFD. It stated that it displays whether the current heading mode is magnetic or true, and the symbology that appears. However, I could not find any place that would allow the pilot to switch between these modes. Is this something a pilot can do, or is it performed internally? If it is performed by a pilot, how do they do it?

This switch is part of the Heading Reference System available only for customers who bought the Polar Operations option.
As the PDMG 737 MAX add-on is not yet available I assume this is for the 737 NG. It seems there are not many 737 NG flying over the poles, and I can't find a picture of the switch.This is where it is on a 757 (see also this):

Source.
Without the option operations at latitudes near or higher than 80° are not possible, as indicated in the 737 Dispatch Deviations Guide (DDG):

In order to conduct polar operations, the HDG REF switch must be installed, and one FMC, one CDU, and GPS-L must be operational for dispatch.

TRUE headings are required at high latitudes, the magnetic declination being not reliable. More.

That picture looks like it's from a 757 or 767, but definitely not a 737 MAX. Are you sure the switch would be located there on the MAX as well?

@Bianfable: No I'm not. Do you have additional information?

No, unfortunately not. As you say, these options are pretty rare for a 737, but I guess some Canadian 737s might have it equipped.

On the 737, it is a customer option associated with polar operations and, if fitted, will be on the overhead just above the window heat switches. If you are interested in polar operations you might find this link interesting: Boeing Polar Operations

Very interesting article.  What year is it from, please?

@RalphJ I think it was originally published in Boeing's "Aero" magazine in 2001.

A reference for the switch location?


text:
Display Unit Options on 737 Next Generation
I was reading the FCOM for the 737 NG, and in the section about the display units I saw these as an option:

It also showed things like single-cue flight directors as well as other things. I have tried to look for these online and have not found any real-life pictures of this type of display unit. Is this a real option, or just very rare?

I think some operators configured this option while they were transitioning from 737 Classics as these displays resemble the older analog instruments and that made it easier for pilots who were still flying both types. I've never seen photos of them either though.

Yeah, it was an option, referred to as the "six pack under glass" -- in other words the 6 round-dial instruments, displayed on a 'glass' display, with what amounts to a half-width Navigation Display inboard of the primary flight instruments (so, to the right of the Captain's altimeter, or to the left of the FO's airspeed indicator).
It allowed for commonality with round-dial 737's that an airline was flying at the same time, so that pilots could operate both the Classics and the Next Gen aircraft without having to be separated into one set of pilots being qualified on the round-dial Classics, while the others were qualified on the PFD/ND Next Gen aircraft.  Being able to use any pilot on any aircraft, or reroute any aircraft to be flown by any crew, simplifies airline scheduling.  And when the 737 NG was first coming out, there were airlines that flew both Next Gen's and Classics that didn't want to separate their crews into two categories, and since the customers asked for it, Boeing obliged.
Once the Classics left the fleet (or maybe even before), the need for this went away, and the alternative of PFD/ND (Primary Flight Display - the ADI with tapes - on the outboard display, and Navigation Display - the map - on the inboard display) became pretty well universal.
The single cue vs dual cue flight director, as I understand it, is simply a switch on the aircraft that maintenance can configure.  Or it may be a different software load.  But that's just a matter of presentation; the underlying flight director logic is still pretty well the same.  Some people prefer one display or the other, but it isn't all that difficult to switch from one to the other -- just takes a little bit of time to get used to whichever one you have.

Have you flown with both single and dual cue FDs? I always found using the single cue much harder to use than the dual cue one.

Flown with both, and I absolutely prefer dual cue. But I've also read comments on another pilot forum by pilots who seem to prefer the single cue. I suspect that those who got lots of experience using single cue before ever having to switch account for much of that.


text:
Function of door in front of nose landing gear bay on the 737
I've been trying to model a 737 as accurately as possible, and I've seen this door in front of the nose landing gear bay a number of times.

I don't know what this door leads to, and I can't find any images that face it head-on so I could possibly read what the labels on the door says. Is anyone aware of what this door does? Thanks!

Which aircraft is that? Classic or NG? It seems this door is the Lower nose compartment access door on both models anyway.

It's called the "E&E Bay," for Electronics & Equipment. Inside are a bunch of black boxes for radios, radar, computers, and so forth. The crew doesn't go there; it's for maintenance. On the walk-around, the pilot checks that the door is closed & the handle is flush, but that's it.
There are two of them, one forward of the nosewheel, another aft of it. There is a door light labeled "EQUIP" that indicates when either door is open, just like a light for each of the forward & after entry and service doors, overwing exits, and so forth. Sometimes you'll see that light come on when maintenance is working on something electronic -- running a BITE test on some computer, replacing a component, or similar.
More info here.

The photo in the OP is a 737 Classic, which has a different layout from the NG. The original photo is here, which identifies it as a 737-300. A similar photo of the door in the same position on a Max-8 is here.

Can you share some diagram for the CL? I've one which also shows the E&E bay on a -300 aft of the NWG doors.

@mins The video in the site that I linked in the answer has those, I believe.

@mins There are two bays. The door asked about in the OP accesses the forward one, while the door aft of the nose gear accesses the main bay. They're both referred to as "E&E bay" by crews; the maintenance techs care about which boxes are in which (obviously), but for crews, they're both doors to reach the same (sort of) thing. The video discusses both bays in this way, as well. (The Boeing graphic shows that there is the aft E&E bay, with the batteries in it, but doesn't exclude the forward bay as having other electronic things. Just not the batteries.)

The second door doesn't seem to be an access to the E&E bay: "The purpose of the lower nose compartment access door is to permit access to the compartment below the flight compartment. Many flight control cables and brake accessories pass through this area."

@mins The FCOM calls the aft one "center electrical and electronic (E/E) equipment access door" and the forward one "equipment compartment access door" (both are connected to the EQUIP light on the flight deck). The video Ralph linked also lists some electrical components in the forward one (PSEU, Fuel Quantity Processor Unit and WX Radar).

@Bianfable: Thanks, that clarifies everything: No opening in direction of the aft E&E bay, and also answers the OP request for the decals on the door.


text:
Calculating best glide speed
I recently started flying a SGS 2-33 glider. The POH lists the stall speed as 31 mph for solo flight. Min sink speed is 38 mph and optimal glide speed is 45 mph.
Being an old glider with imperfections, it stalls at 40 mph.
Knowing that the stall speed is 9 mph higher than described in the POH, how can I calculate a new optimal glide speed?

Perhaps cleaning and waxing the wings (and fuselage) might help.  Effects of a poorly cleaned and scuffed surface are not unlike that of icing.  Also, check to see if the CG is still in the proper range if repairs were made.

I wouldn't fly that glider at all, and tell the owner to red tag it. That is a very large and dangerous difference from the published stall speed at max gross weight for a low performance glider. It could be the airspeed indicator is not operating properly, and needs attention.

If only the maximum lift coefficient suffers from the imperfections, your minimum sink speed is very close to the stall speed and the best glide speed stays unaffected.
If a major mass increase (say, from unprofessional repairs) contributes to the higher stall speed, both the minimum sink and the best glide speed will be shifted to higher flight speeds. Use the dynamic pressure to scale the speeds with the glider's mass.
In general, such an increase in stall speed raises the question if the plane is still airworthy.
The "new" stall speed is at a dynamic pressure which is 66% higher than the old glide speed. This is much more than what could be caused by minor imperfections, so drag should also be affected. To really find out what the new speeds are, you should collect data to plot sink speed over flight speed for the whole speed range. Use early morning aerotows on days with very calm air (caution: High pressure weather means slowly sinking air mass; avoid those days!) and make sure you keep speed constant for as long as possible to measure the altitude loss over time. Correct for density and use the tangent method to find the best glide speed.


text:
Are airport codes with digits valid or pseudo ICAO codes?
Official definition states that an ICAO designator consists of 4 letters (A-Z). But there seems to be quite a lot of airports in the U.S. that don't follow this guideline. Of those, about 300 broadcast an official METAR, which leads me to believe the ID's are genuine.
Does anyone know what the status of these airport designators is, are these actual and valid and official airport codes or just made up and somehow got into the METAR lists?
Couple of examples:
KU42    South Valley Regional Airport
KF70    French Valley Airport
KM01    General Dewitt Spain Airport
K5C1    Boerne Stage Field
K1R8    Bay Minette Municipal Airport
K8D3    Sisseton Municipal Airport
K21D    Lake Elmo Airport
K06C    Schaumburg Regional Airport
KO69    Petaluma Municipal Airport

About the CCCC identifier for the reporting station of TAF/METAR/SPECI: "The TAF code uses the ICAO four-letter location identifiers. In the conterminous United States, the three-letter identifier is prefixed with a K. For example SEA (Seattle) becomes KSEA". SEA, 5C1, 069, etc are FAA local identifiers. Note ICAO only deals with international matters, not with municipal airfields.

No, those are not ICAO codes. ICAO airport identifiers consist of four letters, full stop. But that does not mean that any code which is other-than-four-letters is "invalid" or "unofficial!" There are more standards for identifying airports than just the ICAO code.
As explained in this Av.SE answer, FAA Location Identifiers for airports have the following formats:

Three letters
One number and two letters
One letter and two numbers
Two letters and two numbers

At first blush, some of those K-codes appear to be valid FAA LIDs of that last format... but the four-character FAA LID uses two consecutive letters which are based on the USPS abbreviation for the state where they are located, for example MA or SD. When they run out they can get creative, like IS for Illinois, but KM and KF from your examples do not correspond with any US state.
So as it happens, the identifiers you posted are not valid airport identifiers—not under the ICAO system and not under the FAA system either! Those four-character identifiers beginning with K are National Weather Service identifiers for the weather stations located at various airports. Even though the airports themselves have only an FAA LID, not an ICAO airport code, the NWS identifies all CONUS weather stations using a four-character code prefixed with K. (Note that there does not need to be an airport for there to be a weather station—Mount Washington Observatory is identified as KMWN.) If you strip the leading K from your example identifiers you will discover valid and current FAA LIDs which refer to active airports.
It is true that having an advanced on-airport weather station (and a 5,000' runway) is grounds for assigning a three-letter, rather than letter-number, FAA LID. But if the weather station was added after the fact, the general preference is to keep the LID the same.

Another FAA format is one digit, one letter, one digit -- such as 0S9 (leading zero) for Jefferson County International Airport in Port Townsend, WA. The LID includes a large number of examples in this format. https://www.faa.gov/air_traffic/flight_info/aeronav/aero_data/loc_id_search/Encodes_Decodes/

Yes, that falls under the "one letter and two numbers" format I mentioned.


text:
Why should I request a long landing?
I fly in/out of a small international airport occasionally, the runways are quite long. It is not unusual to land half-way or even three-quarters down the runway.
When doing this, pilots request long landings from ATC. I once did not request a long landing and did anyway and got chewed out a bit from ATC.
My question is:
Is it mandatory to request a long landing or is it more of a courtesy? Where is this information documentated?

One minor point is that "runway behind you" is completely wasted, and if you have an emergency (like a brake failure) then you may wish that you had not landed long...

@Lnafziger, true. For example though, if you're flying a Cessna 150, by-passing 7,000 feet and utilizing the last 3,000 of a runway is still sufficient for any emergency. Just hope them fire-trucks weren't in the first 1,000 feet...

Depending on the way you did it the controller might not have liked the fact that you were very high above the threshold. That, and the time aspect are the only reasons I can think of he might have disliked

I think ATC just wants to know if you are doing anything out of the usual.

There's no mention that I can find of "landing long" ("landing deep" is sometimes used outside the US) in the FAA's P/CG, AIM or ATC procedures. So it's fairly safe to say that it's an unofficial instruction (assuming I didn't miss it somewhere).
The main reason for doing it is to avoid a long taxi after landing, but I suppose there could be other reasons too, like coming in too high on a long runway or avoiding wake turbulence. The point of requesting it - and not just doing it - is that it may mess up sequencing at a busy airport because you take more time to clear the runway, with the result that the tower has to instruct the aircraft following you to go around. As my first instructor said, "once you're cleared to land it's your runway".
I've never been asked by ATC to do it but I have been asked by the tower to "land short", to minimize my time on the runway and let an airline flight take off ASAP. However, it was clearly phrased as an informal request, not an instruction; something like this:

N12345 Clear to land 36L, appreciate a short landing if you can manage it

So I think the conclusion is that landing "short" or "long" is simply an informal way for pilots and ATC to make things work a bit more smoothly.

+1 For having searched the P/CG & ATC procedures. I'd done a word search of the AIM myself because another message board claimed there was something there, but came up empty. In all honesty, the best way to describe it would probably be as aviation jargon; the folks involved all know, in very broad strokes, what you're asking for and what to expect, even if the powers that be never formalized it.

is that it may mess up sequencing at a busy airport because you take more time to clear the runway -- May quite as well be the opposite, depends on the location of suitable taxiways. You are much faster in the air than taxiing a kilometer to the closest exit.

@VladimirF - True. There's also spacing of taxiing traffic to consider, especially at bigger airports that service all kinds. DFW for instance regularly sees everything from little Embraer puddle-jumpers to 747s and A380s. The AmAir Lubbock-DFW red-eye would end up right in the middle of the overnights from Dubai and Berlin, and there's no way the tower would let the regional land deep in that scenario as it means a greater following distance for the jumbo behind it.

However, several regional jets spaced concurrently would have no trouble requesting a deep approach. The tower might even request the jet exit at the far end (either landing deep or just taking its time braking) to better manage jets heading to different terminals.

Yes, the situation I had in mimd happens at LKPR rwy 24 (so not FAA) where small GA's vacate by the same exit (C) as smaller airliners and it is better if they shorten the time to reach that point.

When you are cleared to land, you own the entire runway until you exit.  Use it all if you must.  (One exception to this is at Oshkosh, during the annual AirVenture when as many as three airplanes are cleared to land on the same runway at the same time: one short, one medium, and one long as demarcated by colored dots.)
Having said that, at a busy airport you are expected to land reasonably close to the arrival end, and to exit the runway promptly.  This is an important component of keeping traffic moving smoothly at a busy airport, so if you want to land long you should inform the tower of your request.
A good reason to land long:  If the controller has positioned you too close behind a large airliner so that wake turbulence is an issue, tell the controller that you want to land long.  Wingtip vortices stop as soon as the aircraft lands, and you want your touchdown point beyond the large airliner's touchdown point.

I don't think it is documented anywhere that you must inform the controller if you want to land long. But you should state your intentions clearly as a courtesy to the controller and by effect other aircraft that you share the airport with.
The controller will expect a small aircraft to take the first runway exit. They plan the arrival stream accordingly. From experience they know it will take a Cessna 150, for example, 40 seconds between overflying the threshold and vacating at the first exit. Thus they can space the next aircraft appropriately so that they can give a landing clearance in time after you vacate.
When you unexpectedly fly all the way to the second half of the runway before landing it will take much longer between overflying the threshold and vacating the runway. This will make the margins for giving the landing clearance to the aircraft behind you much smaller and may even force the controller to order the big jet on your tail to go around.
For screwing up somebody else's plan and causing others to go-around you get shouted at sometimes.

Long landings are requested mostly by GA pilots (although airlines can do it too) on longer runways. ATC is informed about it.
If the aircraft is parked near the end of the runway, or needs to get there, long landing is used as it is faster to fly at 80 knots than to taxi at a much lower speed.
I'm not sure why ATC didn't like it in your particular situation. It could be that they were expecting you to get off the runway sooner, which you didn't.
This PDF explains this. I couldn't find any regulations related to it.

For your last point, I think OP landed long without requesting it from ATC

Same reason you can do intersection takeoffs.  If you're parked at midfield, why taxi half a mile when you only need about 1000 ft of runway?

The link to the PDF is a 404.

In EASA land, you can also be asked to make a long landing because the controller will want to clear another aircraft to land behind you, although you are still occupying the runway. This tool is called Reduced Runway Separation and requires the preceding aircraft to be beyond a certain distance measured from the runway threshold, before the subsequent approaching aircraft can be cleared to land.
Related question:
When is an aircraft cleared to land?

ATC doesn't like unannounced long landings because unless they are informed of what you're doing, they will be concerned that you're just too fast or too high and might run off the end of the runway.

authors: Vladimir F Героям слава


text:
Is military grade jet fuel more expensive than civilian grade?
Is military grade jet fuel more expensive than civilian grade?
Why are governments moving away from military grade jet fuels?

@fooot Not quite duplicate. The cost is not takled in the linked question (but yes all the other aspects of the question are answered there).

Related: Why do military aircraft use a different kind of aviation fuel?

Prices
Relative prices depend on what military fuel you compare to what civilian fuel. The current US Defense Logistics Agency pricing for jet fuels is as follows:
    Fuel type     $/gallon $/barrel
    JP8 & JA1     2.15     90.30
    JAA           2.13     89.46
    JP5           2.18     91.56

JA1 is "Jet A1"--normal, internationally available civilian jet fuel.
JAA is "Jet A with Additives". It's Jet A (which is slightly less expensive than Jet A1, but available primarily in the US) with some additives added to improve lubrication, reduce corrosion, icing, etc.
JP8 is the jet fuel the US military used for years before (semi-recently) switching to mostly using civilian grades. Basically Jet A1 plus some additives.
JP5 is used primarily aboard aircraft carriers. It has slightly higher density than the others, and a substantially higher flash point (>= 60C, vs. >= 47C for Jet A1/JP8).

Summary
The military designations are mostly slightly more expensive than their purely civilian-grade counterparts. The prices given above are also somewhat higher than the IATA shows for pricing on jet fuels in the general market, at least at this moment1.
Why
Part of the reason for moving to civilian fuels is to reduce costs. Along with that, using something that's widely used and available makes it much easier to manage the supply chain, ensure an adequate supply, etc.
References

Defense Logistics Agency FY 2018 Fuel Prices
JP-8 and other Military Fuels (Warning: PDF)
IATA Jet Fuel Price Monitor

1. At least as I read things, the price given by the DLA is intended to be used for budget estimates, so it presumably reflects their worst-case estimate of the average price during the coming year.

JA1 is formulated for colder environments than JA. Also some of the reason for having both military and civilian formulas goes way back to a time before either had a common standard so they each invented their own. Also military secrecy around any new tech may have played some role. having slightly different grades may also make investigating quality control and tracking sources and batch issues easier.